In general, a check valve is mounted on a fuel tank of an automobile or the like, the check valve being arranged to make a fuel vapor flow outside to prevent the fuel tank from bursting when the pressure in the fuel tank rises to a predetermined value or more. On the other hand, intake of the outer air from the outside of the fuel tank prevents the fuel tank from being crushed when the pressure in the fuel tank falls to a predetermined value or less with respect to outside air pressure.
For example, WO-2010-064475-A discloses a check valve that includes a casing main body including a positive pressure valve seat inside, a sub-casing, a positive pressure valve including a negative pressure valve seat, and a negative pressure valve attached to the positive pressure valve seat. A positive pressure spring to urge the positive pressure valve toward the positive pressure valve seat is provided between the positive pressure valve and the sub-casing. The positive pressure valve is arranged to move away from the positive pressure valve seat when the pressure in a fuel tank rises to a predetermined value or more. The negative pressure valve is arranged to move away from the negative pressure valve seat when the pressure in the fuel tank falls to a predetermined value or less.
The positive pressure valve has a cylindrical shape extending long enough to cover the entire circumference of the positive pressure spring. Spring holding ribs protrude on the inner circumference of the positive pressure valve. The positive pressure spring is supported by the sub-casing at the base end, and the distal end is inserted into the positive pressure valve. The positive pressure spring is held by the spring holding ribs in the predetermined range from the distal end without inclination.
In the check valve, the positive pressure valve is configured to slide inside a valve case to abut on and separate from the positive pressure valve seat. To precisely set the pressures at which the positive pressure valve abuts on and separates from the positive pressure valve seat, the positive pressure spring needs to be disposed without inclination with respect to the axial center of the valve case. This is because, if the positive pressure spring is inclined, the urging force of the positive pressure spring could change.
However, in the case of the check valve of WO-2010-064475-A, the positive pressure spring is partially inserted into the inner circumference of the positive pressure valve in the predetermined range from the distal end, which holds the positive pressure spring at the spring holding ribs. Therefore, if the positive pressure valve is inclined, the positive pressure spring is also inclined accordingly. This may affect the opening responsiveness of the valve.